The present invention relates generally to electronic devices and, more particularly, to a voltage supply device of a control device that is mounted in a motor vehicle and that comprises a logic unit, used mainly for processing information, and a power unit, used mainly for driving the actuators.
Modern motor vehicles exhibit a large number of control devices, which under some circumstance continue to consume energy even while the motor vehicle is standing still. In particular, in the case of a malfunction of one or more control devices, this energy consumption may put an extremely high load on the vehicle battery of the motor vehicle, and with time the battery may be exhaustively discharged. Since the control devices are typically linked together by way of a databus, a fault in a single control device may also lead to an enhanced energy consumption of the other control devices.
The most common reasons for an exhaustive discharge of the battery of a motor vehicle include the following cases:
In a first case, due to a defect, a control device does not report its inactivity to the databus. All other control devices also remain active and, therefore, have an energy consumption that is higher than in the off state. In this way, the vehicle battery may be loaded with a steady current of several amperes (e.g., 5 A).
In another case, due to a defect, a control device repeatedly sends wake-up signals to all of the other control devices, connected to the databus. These control devices thus change repeatedly into an active state and have an energy consumption that is higher than in the off state. Even such defects may result in current being drawn from the vehicle battery. This current may be in the ampere range (e.g., 1 A) in the time average.
In another case, due to a defect, the processor of a control device performs enhanced computational services without simultaneously influencing other control devices. In this case, the resulting additional current drain from the vehicle battery may be in the range of several hundred milli-amperes (e.g., 200 mA).
A variety of devices exist by which an exhaustive discharge is avoided by separating the individual consumers, all consumers or groups of consumers from their voltage supply. The separation is typically carried out by opening a switch unit (e.g., a monostable or bistable relay), which is provided in the supply line of one or more control devices. The separation may be effected in a time-controlled manner, an event-controlled manner or—as known, for example, from the DE 19922331 C1—upon the request of a user.
In the design of the majority of the control devices currently installed in motor vehicles, one can distinguish between a logic part, used mainly for processing information, and a power part, used mainly to drive the actuators. In conventional systems, both parts are supplied with voltage from a common supply line. When the switch unit is closed and the control devices are operating, the sum of the useful currents of all of the control devices, which are supplied by this supply line, flows over such a supply line. Thus, the switch unit is designed in such a manner that it can be loaded with the maximum value of the sum of useful currents, flowing over the respective supply line.
Specific functionalities of modern motor vehicles (e.g., activation) require useful currents of up to 40 A just for a single control device. A corresponding design of the switch units may be technically feasible, but is associated with high production costs. Therefore, a drawback of conventional systems lies in the fact that the switching off in the sense of preventing the current from being drawn from a voltage source by a control device having a high useful current requirement by opening a switch unit is realizable only at a very high cost.
An aspect of the invention is to provide an inexpensive device, which may be achieved with a low complexity in design and which prevents in an efficient way the current from being drained from a voltage source by a defective control device.
Consistent with the present invention, separate supply lines are provided for the voltage supply of the part (logic unit) used mainly for processing information and for the part (power unit) used mainly to drive the actuators of a control device, and only the supply line of the logic unit is provided with a switch unit.
One advantage of the invention lies in the fact that the switch unit, provided in the supply line of the logic unit, is designed for a load of significantly lower current intensities and thus may be realized at a considerably lower cost.
The cause of the majority of the faults occurring in control devices and relevant to an exhaustive discharge of the vehicle battery lies in a defective processing of information. The fault cases described above document this situation. To prevent in an efficient way the current drain by a defective control device, it is sufficient to separate its logic unit from the voltage supply. Hence, the control device is put into a state, in which the power unit is, in fact, supplied with voltage, but does not draw any current.
The circuit-relevant division into a logic unit and a power unit is already executed in the majority of the control devices used today, or may be achieved with a low complexity in design. The interconnection may be carried out in such a manner that the power unit may draw current only if the power unit is also supplied with voltage. The design, production and material costs for the variant with separate supply lines, instead of a common supply line, are ignorable, compared to the savings that can be achieved by the modified load on the switch unit, especially in motor vehicles with a plurality of installed control devices.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.